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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> Output swing of VCO inverter chain https://designers-guide.org/forum/YaBB.pl?num=1168869854 Message started by adesign on Jan 15th, 2007, 6:04am |
Title: Output swing of VCO inverter chain Post by adesign on Jan 15th, 2007, 6:04am Dear all, I'm designing a ring-oscillator with 5 inverter stages(current starved inverters). Each inverter stage has two current sources. One is to charge the capacitor formed by the next stage and the other is to discharge that. Both the current sources have the same dc current level.(The basic schematic is attached herewith for one of the inverter stage). For keeping both the current sources(top and bottom) in saturation, we need to limit the swing of the inverter chain. I'm trying to reduce that by reducing the length as well as reducing the current supplied by the sources. However, I've reached the limit of minimum length of the devices. I'm also seeing that whenever the output frequency is high then the swing is limited whereas when the output frequency is low the swing is very high(almost rail-to-rail). Could you please suggest me any alternate way to reduce the swing or to keep the sources in saturation? Best regards, |
Title: Re: Output swing of VCO inverter chain Post by jeffyan on Jan 15th, 2007, 11:06pm adesign wrote on Jan 15th, 2007, 6:04am:
hi, i think you can try to add a diode connection mos transistor onto the output. in this way, the tail current can keep acting as a current source. this is an original idea, which is not suitable for your case. but after some modification, you can realize a good clipping swing. good luck jeff |
Title: Re: Output swing of VCO inverter chain Post by topquark on Jan 16th, 2007, 12:33am Yes, the current sources could be derived from a mirror, both for the PMOS and the NMOS. But, I don't see why you need to reduce the output swing which would only worsen your phase noise. Any other design criteria you're after? Regards, Gau |
Title: Re: Output swing of VCO inverter chain Post by adesign on Jan 16th, 2007, 1:05am Hi, The current sources are derived from a mirror itself. However, for the large swings, both the current-sources may go into linear. This is the only concern I have. Please comment. Regards, |
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